Toothpaste composition

ABSTRACT

Packaged toothpaste formulations which contain air sensitive components, e.g. vitamin C, are prevented from discoloring or otherwise degrading, by placing adjacent to an area of the packaging which may allow air access to the formulation, e.g. an air permeable collar, a nozzle, or the wall of an air permeable tube, a body (e.g. plug or layer) of material which does not contain any air sensitive components. Preferably, the latter body of material is the packaged toothpaste but without the air sensitive components.

FIELD OF THE INVENTION

This invention relates to toothpaste compositions which contain airsensitive molecules which show a tendency to degrade upon exposure Toair, leading to deleterious effects such as discolouration, loss orspoiling of flavour or the like. The invention also relates to methodsfor the prevention of such air-induced degradation.

BACKGROUND OF THE INVENTION

It is frequently desirable to incorporate into toothpaste formulationscertain molecules which may often be air sensitive, for example vitaminC. Often the degradation products produced on exposure of the toothpasteformulation to air are a different colour to the original compound; inthe case of vitamin C its air decomposition products are coloured brown.Hence it has been a major disincentive to manufacturers who would wishto incorporate such air sensitive compounds in toothpaste formulationsthat such pastes tend to discolour after a period of time, therebyappearing visually unattractive to a potential user. Similar problemsmay occur with other air sensitive substances such as certain flavourmolecules or pharmaceuticals, which upon air-induced degradation resultin impairment or even loss of the respective desired properties of thetoothpaste.

Such problems have been partially overcome by the use of air impermeabletubes. Traditional tubes such as those made from metals such asaluminium are regarded by consumers as old fashioned, and also thesetubes are not ideal from other perspectives, as they tend to crack afterextended use, thereby causing the toothpaste to leak. Paint on thesurfaces of these tubes also tends to crack and flake off upon extendeduse.

Plastics tubes now enjoy popularity. However, these also havedisadvantages, since they are prone to the permeation of air through thetube and into the contents, and also the permeation of volatilesubstances in the paste out of the tube, with the result that thetoothpaste shows a tendency to discolour and/or lose flavour or otheractive properties on storage. Air impermeable plastics tubes have beendeveloped to overcome these problems, and have in general beensuccessful in preventing air gaining access to the toothpaste. Suchsolutions to these problems are not without their own problems though;an air impermeable tube costs typically 3-10 times the amount of anordinary plastic tube.

Laminated tubes, for example tubes containing a metal layer such asaluminium laminated between two layers of a plastics material such aspolyethylene, have also been developed which in practice have most ofthe advantages of both plastic and metal tubes. Such tubes areeffectively air impermeable, and are the generally preferred choice ofmanufacturers in which to pack toothpaste for commercial sale.

However, because of technical problems associated with the assembly ofsuch tubes, complete tubes made entirely of laminated material have notbeen available. In practice, sleeves of laminated tube material are heatsealed to a preformed plastics collar nozzle assembly which is sealed bya plastics cap. Toothpaste is then dosed into the other open end, whichis then crimped or otherwise sealed. The toothpaste can then bedispensed through the preformed nozzle.

Overall it has not been possible to totally prevent toothpaste containedin tubes from coming into contact with air. Where this is caused by theingress of air on prolonged storage, it is observed that most of thisingress occurs through the collar of the tube; the toothpaste is alsoexposed to the small amount of air that typically remains in the nozzlearea of the tube after it has been filled. The problem is exaggerated ifthe filling of the tube does not occur uniformly, as is bound to happenoccasionally in the mass manufacture of packaged toothpaste. In suchcircumstances, small unwanted air voids will be trapped in thetoothpaste, usually adjacent the collar/nozzle assembly, after filling.This is still a general problem for toothpaste manufacturers since itcan lead to dehydration, discolouration and flavour loss from the paste,in particular in parts of the tube near the collar. The problem isparticularly acute for the manufacturer of toothpaste who wishes toinclude air sensitive compounds in a toothpaste formulation, such as forexample vitamin C. It is found that after storage such vitamin Ccontaining toothpaste formulations discolour in the vicinity of the tubecollar; hence the first few centimeters of the toothpaste that aredispensed are discoloured. Such a product is obviously qualitysuspicious to the consumer, if for example the bulk of the toothpaste iscoloured white but the first few centimeters are coloured brown.

It has also been observed that even if formulations containing airsensitive compounds such as vitamin C are stored in special tubes whichhave been made air impermeable, the surface of the paste which is incontact with the air contained in the aforementioned nozzle gap rapidlyturns brown. Hence, even the provision of totally air impermeable tubeswould not totally solve the problem, whilst using current technology themost cost effective toothpaste packaging is not totally air impermeable.

Hence there exists a need for a method of packaging toothpaste whichcontains air sensitive components which prevents the discolouration orother form of degradation of such toothpaste caused by exposure of areasof the toothpaste to air. The problem is noticeable even when airimpermeable packaging is used, but is particularly noticeable when thepackaging used is not totally air impermeable, for example if aneffectively air impermeable laminated toothpaste tube is fitted with anair permeable (e.g. polyethylene) collar.

It is known in the art to provide different reactive components of atoothpaste composition which are to be reacted together in use inseparate compartments of a toothpaste package, which two components arebrought into contact with each other for reaction together at the timeof dispensation from the package. Examples of such known systems aredescribed in GB-A-1561418 and GB-A-2112642. These systems however do notaddress the problem of air-induced degradation of either of the reactivecomponents, or indeed other components of the toothpaste composition.

SUMMARY OF THE INVENTION

We have surprisingly found that a solution to the problem of degradationof toothpaste formulations which contain one or more air sensitivecompounds is to place, when filling the tube and adjacent to the area orareas of the tube through which air may gain access, a body of materialwhich does not contain any air sensitive compounds. The air-sensitivecompound-free body of material may for example be in the form of a plugor lining layer, or even a combination of the two.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In a preferred solution, the body of material which does not contain anyair sensitive compounds is another toothpaste formulation, preferably aplug or layer of toothpaste formulation which is identical to the firsttoothpaste formulation except that it does not contain the air sensitivecompound or compounds.

The invention also provides a packaged toothpaste formulation comprisinga toothpaste tube, a toothpaste composition containing one or more airsensitive compounds, and a toothpaste composition not containing any airsensitive compounds.

In a preferred embodiment, the toothpaste composition not containing airsensitive compounds is located in a toothpaste tube adjacent to theparts of the package which may either trap air or allow the ingress ofair, and the toothpaste composition containing the air sensitivecompound(s).

In the case of toothpaste formulations which contain vitamin C forexample, this means placing a layer of the same toothpaste formulationbut which does not contain vitamin C adjacent to any areas of thepackaging through which air may gain access. This may be for exampleadjacent to the collar of the tube if a tube is used which has an airimpermeable laminated body and an air permeable collar, and/or adjacentto the nozzle area of the tube where an air gap may exist after filling.Additionally or alternatively, it may include coating substantially thewhole internal area of an otherwise empty air permeable toothpaste tubewith the same toothpaste formulation but which does not contain any airsensitive compounds, if the body of the toothpaste is to contain the airsensitive compound(s).

In a preferred embodiment of the invention, in particular where thetoothpaste not containing air sensitive compounds is a plug adjacent tothe collar of the tube, the toothpaste not containing air sensitivecompounds comprises 1-20% of the total amount of the toothpasteformulation, more preferably 4-13% of the total amount of the toothpasteformulation.

Toothpastes made according to the method of the invention have provedremarkably resistant to degradation by air on storage. This invention isall the more surprising since if the body of material not containing theair sensitive component adjacent to the air permeable packaging elementis an identical toothpaste formulation, except that it does not containthe air sensitive component, and degradation is detected for example bydiscolouration, one would expect some degree of discolouration to occurin the layer not containing the air sensitive component since many airsensitive components are mobile in the toothpaste formulation matrix.Therefore, one would expect the air sensitive components to spread intothe part of the formulation not containing them (i.e. adjacent to theair permeable packaging) and cause some discolouration there, but thishas been observed only to occur at a very slow rate.

When used in conjunction with preferred toothpaste tubes which, as hasbeen previously explained, comprise a laminated body and an airpermeable collar, the invention provides an extremely convenient andcost effective way of packaging toothpastes the bulk of which containone or more air sensitive materials.

The part of the toothpaste formulation not containing air sensitivecompounds can in a preferred embodiment also act as a matrix in whichoxygen scavenger compounds, such as stannous compounds or sodiummetabisulphite, may be contained. This further increases the plug's orlayer's effectiveness in preventing degradation.

A preferred method of manufacture of packaged toothpaste according tothe invention is to provide a laminated tube body with an air permeablecollar already sealed to it by conventional techniques, positioned suchthat the unsealed tube end is located vertically above the air permeablecollar. The toothpaste composition not containing air sensitivecompounds can then be dosed into the tube, followed by the bulk of thetoothpaste which does contain air sensitive compound(s). The open end ofthe tube can then be crimped or otherwise sealed by conventionaltechniques.

When used in combination with other methods of preventing air ingressinto toothpaste formulations, such as for example utilising totally airimpermeable packaging, the method of the invention can provide aparticularly effective way of preventing the degradation of airsensitive compounds in toothpastes.

The present invention may be used to prevent or inhibit air-induceddegradation in packaged toothpaste of a variety of substances whichimpart desirable properties, yet which tend to result in deleteriouseffects such as discolouration, loss of colour, loss or impairment offlavour or pharmaceutical activity, when subjected to prolonged exposureto air, especially at relatively high storage temperatures.

In addition to vitamins such as vitamin C, other substances to which theinvention may be usefully applied include for example the following:

other ene-diols (vitamin C is an example of such a compound)

catechols

tannins

metal salts in low oxidation states which change colour onair-oxidation, e.g. ferrous salts

iodide salts

flavour molecules which are susceptible to loss of or change in flavourupon air-oxidation.

The invention will now be illustrated with reference to the followingexamples.

EXAMPLE 1

The following basic toothpaste formulation was prepared:

    ______________________________________                                        Component          % w/w                                                      ______________________________________                                        Silica             18.5                                                       Sorbitol (70% solution)                                                                          45.0                                                       Polyethylene glycol                                                                              5.0                                                        Flavour            1.4                                                        Binder             0.9                                                        Whitener           1.0                                                        Sodium fluoride    0.22                                                       Sodium lauryl sulphate                                                                           1.875                                                      Water              to 100                                                     ______________________________________                                    

For the purpose of the comparative storage test, to the basicformulation was added vitamin C and stannous pyrophosphate (which canact as both an oxygen scavenger and a stabilizing agent for vitamin C).A further suitable oxygen scavenger is sodium metabisulphite.

    ______________________________________                                                      Weight %                                                                               "Body" toothpaste                                      Formulation     Plug   formulation                                            ______________________________________                                        I     stabilizing agent                                                                           0      0                                                        vitamin C     0      0.25                                               II    stabilizing agent                                                                           1      1                                                        vitamin C     0      0.25                                               III   stabilizing agent                                                                           1      0                                                        vitamin C     0      0.25                                               ______________________________________                                    

All the figures are % w/w of the formulation. Each tube was dosed with75 g of toothpaste formulation in total, of which the plug (if present)comprised 7.5 g. The formulations were dosed into laminated tubes, withthe plug (if present) adjacent the collar part of the tube, and sealedby conventional techniques. The tubes were then subjected to elevatedtemperature storage tests at 37° C. and 50° C. to simulate longer termstorage conditions. After periods of 5 weeks and 3 months, the sampleswere inspected for browning both by squeezing out a ribbon of paste, andalso by cutting open the tube and viewing the contents.

The discolouration of the pastes in the tubes was assessed according tothe following scale:

    ______________________________________                                        Grade         Description                                                     ______________________________________                                        0             No colour change                                                1             Detectable colour change, not                                                 noticeable in normal use                                        2             Detectable colour change, may                                                 be noticeable in normal use                                     3             Detectable colour change,                                                     clearly visible, no browning                                    4             Mild browning                                                   ______________________________________                                        Results                                                                                         Colourchange                                                                  5 weeks  3 months                                           Temperature                                                                             Formulation                                                                              Plug   Neck Body  Neck Body                              ______________________________________                                        50° C.                                                                           I          No     3    0     3    1                                                      Yes    0    0     1    1                                           II         No     0    0     2    0                                                      Yes    0    0     1    0                                           III        No     0    0     4    0                                                      Yes    0    0     2    0                                 37° C.                                                                           I          No     2    0     3    1                                                      Yes    0    0     2    1                                           II         No     0    0     1    0                                                      Yes    0    0     0    0                                           III        No     0    0     3    0                                                      Yes    0    0     0    0                                 ______________________________________                                    

These results clearly show that discolouration of toothpasteformulations in parts of the tube where air may permeate or be otherwisepresent is improved (both in stabilized and unstabilized formulations)if a plug is used which does not contain the air sensitive compoundsfound in the body of the paste.

We claim:
 1. A method for preventing a packaged toothpaste formulationcontaining at least one air sensitive component from degrading throughcontact with air, said formulation held within packaging comprising alaminated tube with an air permeable collar, said method comprisingplacing adjacent to said air permeable collar a plug or layer of saidformulation absent said at least one air sensitive component.
 2. Amethod according to claim 1, wherein said packaged toothpasteformulation further comprises an oxygen scavenger compound present in aneffective amount to prevent degradation of said at least one airsensitive component.
 3. A method according to claim 2, wherein saidoxygen scavenger compound is selected from the group consisting ofstannous compounds and sodium metabisulphite.
 4. A method according toclaim 1, wherein said packaged toothpaste formulation absent said atleast one air sensitive component comprises from 1 to 20% of totalamount of said packaged toothpaste formulation held within saidpackaging.
 5. A method according to claim 1, wherein said packagingincludes a nozzle via which said toothpaste formulation is dispensed andsaid plug or layer of said toothpaste formulation absent said at leastone air sensitive component is placed adjacent to said nozzle.
 6. Amethod according to claim 1, wherein said air sensitive component isselected from the group consisting of: ene-diols; vitamins; catechols;tannins; metal salts in low oxidation states which change colour onair-oxidation; iodide salts; flavour molecules which are susceptible toloss of or change in flavour upon air-oxidation; and mixtures thereof.7. A method according to 1, wherein said air sensitive component isvitamin C.